From the viewpoint of excellent charge and discharge cycle characteristics and current efficiency, attention is directed to fluorinated 1,3-dioxolan-2-one (hereinafter also referred to as “fluorinated EC”) represented by 4-fluoro-1,3-dioxolan-2-one (hereinafter also referred to as “F-EC”) as a solvent for an electrolytic solution to be used on electrochemical devices such as secondary batteries and capacitors. For example, Patent Document 1 discloses that lithium ion secondary battery using this compound as a solvent is excellent in charge and discharge efficiency and exhibits good charge and discharge cycle characteristics as compared with secondary batteries using a solvent not subjected to substitution with fluorine.
Examples of known processes for preparing fluorinated EC are:    (1) a process for directly fluorinating 1,3-dioxolan-2-one as a starting material with fluorine gas, and    (2) a process for substituting halogen atom (Cl, Br or I) of halogenated (with Cl, Br or I) 1,3-dioxolan-2-one (hereinafter also referred to as “halogenated EC”, which does not include the target “fluorinated EC”. hereinafter the same) with fluorine atom by using, as a fluorinating agent, metallic fluoride in nearly an equivalent amount (Patent Documents 2 to 4).
Patent Document 2 describes that 4-chloro-1,3-dioxolan-2-one (hereinafter also referred to as “Cl-EC”) and potassium fluoride were mixed and reacted, and F-EC was obtained at yield of 70%. However, fundamental conditions such as a reaction solvent, reaction temperature and reaction time are not disclosed.
In Patent Documents 3 and 4, Cl-EC was reacted with 1.2 equivalent of potassium fluoride in acetonitrile at 80° to 85° C. for 11 hours, and a crude product of F-EC containing Cl-EC of a starting material was obtained at yield of 87.5% (by re-crystallization, F-EC can be obtained at 85% of the crude product).
However, in the processes for preparing fluorinated EC disclosed in Patent Documents 2 to 4, the reaction is a solid-liquid reaction using, as a fluorinating agent, a solid metallic fluoride represented by potassium fluoride, and therefore, metallic fluoride having a large surface area is necessary for increasing a reaction speed and also a step for removing solids is required.    Patent Document 1: JP62-290072A    Patent Document 2: WO 98/15024    Patent Document 3: JP2007-8826A    Patent Document 4: JP2007-8825A